Viruses are the most abundant biological entities on Earth, and are classified by the Baltimore Scheme into seven genomic groups based on the chemical type, number of strands, and strand translation ability of each virus: I: dsDNA viruses, II: ssDNA viruses (+strand or “sense”) DNA, III: dsRNA viruses, IV: (+)ssRNA viruses (+strand or sense) RNA, V: (−)ssRNA viruses (strand or antisense) RNA, VI: ssRNA-RT (reverse transcriptase) viruses (+strand or sense) RNA with DNA intermediate in life-cycle, and VII: dsDNA-RT (reverse transcriptase) viruses. Each group contains enveloped and non-enveloped viruses, which share similar behavioral and structural similarities.
Viruses infecting domesticated and wild animals pose substantial economic and sustainability threats to commercial operations and natural ecosystems. Many viruses can be spread without direct contact between infected animals and potential hosts, such as epizootic hemorrhagic disease (EHD) which is spread by biting midges, and accordingly can rampantly spread through captive populations and wild ecosystems regardless of host animal proximity. In an example, porcine reproductive and respiratory syndrome (PRRS) became pandemic in the 1990s and has caused an estimated annual economic loss of $600 million in the United States. In equine populations, equine herpesvirus-1 (EHV1) can cause spontaneous abortion of foals, respiratory infection, and neurological symptoms.
Viral infections of animals have been combatted with vaccines and pharmaceuticals, which require evaluation and approval from the USDA, FDA, and EPA. However, viral mutations can render many of these treatment methods ineffective. Further, inadequate resources and delayed regulatory approval can hinder vaccine and pharmaceutical development necessary to pace with viral mutations. Vaccines and pharmaceuticals can also persist in the environment almost indefinitely, and bioaccumulate to dangerous levels. Moreover, many antiviral treatments are inherently detrimental to host subjects, but are used due to the absence of alternatives. Human immunodeficiency treatments are an example, which are not capable of completely eliminating HIV from the host subject, yet leave the host subject body and immune system in a weakened state.